Ronaldo "Jacare" Souza is a Brazilian Mixed Martial Arts (MMA) fighter, Submission Grappler and Brazilian Jiu-Jitsu practitioner. Jacare started training Brazilian Jiu-Jitsu when he was 17 years old living in Manaus, Brazil. His nickname "Jacare" means alligator in Portuguese.

Jacare is the 2004 and 2005 Openweight World Jiu-Jitsu Champion, the 2005 77–87 kg ADCC Champion and the 2005 ADCC Absolute Division runner-up, only losing to Roger Gracie who outweighed him by approximately 25 lb. In 2008, he became the runner-up in the DREAM Middleweight Grand Prix tournament, after losing to Gegard Mousasi in the finals. After the DREAM tournament, Mousasi would relinquish the middleweight title after deciding to compete in a hugher weight class. Jacare would then rematch Jason "MayheM" Miller, who he defeated in the second round of the DREAM tournament, to determine the new DREAM middleweight champion. The match took place in MAy 2009 and was ruled a "no contest" after MayheM opened a cut on Jacare with an illegal kick. In September of 2009, Jacare would compete in a Superfight at the 2009 ADCC World Championships as a late injury-replacement for Roger Gracie. Jacare would defeat Robert Drysdale via points (2-0) due to a takedown. Jacare recently signed with Strikeforce and will comepete in their middleweight division.